1. Field of the Invention
The invention relates generally to an electrophysiological (xe2x80x9cEPxe2x80x9d) catheter for providing energy to biological tissue within a biological site, and more particularly, to an EP catheter with a platelet inhibitor substance stored therein that becomes eluted upon contact with biological fluid and thereby prevents the formation of coagulum and other substances from adhering to the catheter surface during an ablation procedure.
2. Description of the Related Art
The heart beat in a healthy human is controlled by the sinoatrial node (xe2x80x9cS-A nodexe2x80x9d) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (xe2x80x9cA-V nodexe2x80x9d) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth, remodeling, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as xe2x80x9ccardiac arrhythmia.xe2x80x9d
While there are different treatments for cardiac arrhythmia, including the application of anti-arrhythmia drugs, in many cases ablation of the damaged tissue can restore the correct operation of the heart. Such ablation can be performed percutaneously, a procedure in which a catheter is introduced into the patient through an artery or vein and directed to the atrium or ventricle of the heart to perform single or multiple diagnostic, therapeutic, and/or surgical procedures. In such case, an ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. A widely accepted treatment for arrhythmia involves the application of RF energy to the conductive tissue.
In the case of atrial fibrillation (xe2x80x9cAFxe2x80x9d), a procedure published by Cox et al. and known as the xe2x80x9cMaze procedurexe2x80x9d involves the formation of continuous atrial incisions to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. While this procedure has been found to be successful, it involves an intensely invasive approach. It is more desirable to accomplish the same result as the Maze procedure by use of a less invasive approach, such as through the use of an appropriate EP catheter system providing RF ablation therapy. In this therapy, transmural ablation lesions are formed in the atria to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. In this sense transmural is meant to include lesions that pass through the atrial wall or ventricle wall from the interior surface (endocardium) to the exterior surface (epicardium).
During ablation, RF energy is applied to the electrodes to raise the temperature of the target tissue to a lethal, non-viable state. In general, the lethal temperature boundary between viable and non-viable tissue is between approximately 45xc2x0 C. to 55xc2x0 C. and more specifically, approximately 48xc2x0 C. Tissue heated to a temperature above 48xc2x0 C. for several seconds becomes permanently non-viable and defines the ablation volume. Tissue adjacent to the electrodes delivering RF energy is heated by resistive heating which is conducted radially outward from the electrode-tissue interface. The goal is to elevate the tissue temperature, which is generally at 37xc2x0 C., fairly uniformly to an ablation temperature above 48xc2x0 C., while keeping both the temperature at the tissue surface and the temperature of the electrode below 100xc2x0 C. In clinical applications, the target temperature is set below 70xc2x0 C. to avoid coagulum formation. Lesion size has been demonstrated to be proportional to temperature.
Blood coagulation is a major limitation/complication associated with RF ablation therapy. Coagulation can lead to thromboembolism and can also form an insulating layer around the electrode hindering further energy delivery required for ablation therapy. Heat appears to be a major factor in the formation of blood coagulum on a catheter electrode. During a typical RF energy ablation procedure using an EP catheter, on or more electrodes carried by the catheter are positioned such that a portion of the electrodes are in contact with the tissue being ablated while the remaining portion of the electrodes are in contact with blood. The RF energy applied during the procedure resistively heats the tissue which in turn heats the electrode through conduction. As blood stays in contact with the heated electrode, platelet activation occurs. This platelet activation appears to lead to coagulum formation.
Hence, those skilled in the art have recognized a need for providing a catheter with a platelet inhibitor substance dispersed therein that becomes eluted upon contact with biological fluid and thereby prevents the formation of coagulum and other substances from adhering to the catheter surface during an ablation procedure. The invention fulfills these needs and others.
Briefly, and in general terms, the invention is directed to an ablation catheter having a platelet inhibitor substance dispersed therein that becomes eluted upon contact with biological fluid and thereby prevents the formation of coagulum and other substances from adhering to the catheter surface during an ablation procedure.
In a first aspect, the invention relates to a catheter for use within a body cavity having biological fluid therein. The catheter includes a shaft having a proximal end, a distal-end region and an outside surface. At least one pocket is carried by the shaft and has an opening terminating at the outside surface of the shaft. The catheter also includes a soluble platelet inhibitor substance within the at least one pocket that is adapted to pass through the pocket opening upon contact with the biological fluid. By incorporating a platelet inhibitor substance within the pocket opening for the subsequent elution thereof, adhesion of blood platelets on the surface of the catheter is prevented or at least substantially minimized. Accordingly, coagulum causing components of the blood cannot contact the catheter surface and coagulation cannot begin and hence, not propagate.
In a detailed aspect, the platelet inhibitor includes heparin, glycoprotein IIb/IIIa inhibitor and aspirin. In another detailed aspect, the shaft has a tubular wall which carries the at least one pocket. In yet another detailed aspect, the at least one pocket is within the tubular wall. In a further detailed aspect, the at least one pocket is within the lumen defined by the tubular wall. In another detailed aspect, the shaft further includes at least one electrode that carries the at least one pocket. In other detailed aspects, a layer of a platelet inhibitor substance is posited on an outside surface of the shaft. Alternatively, a layer of a heparin and sugar-based solution mixture is deposited over the outside surface of the shaft with the layer adapted to dissolve into the biological fluid. In a further detailed aspect, the solubility of the platelet inhibitor substance increases with temperature through application of RF energy by an RF generator to the catheter surface.
In a second aspect, the invention relates to a catheter system for use within a body cavity. The catheter system includes a shaft having a proximal end and a distal-end region. The shaft carries a lumen network having a proximal opening that communicates with a source of platelet inhibitor solution and at least one distal opening that is adapted to terminate at the outside surface of the shaft. The catheter system further includes a first mechanism adapted to force the platelet inhibitor solution from the source through the at least one distal opening of the lumen network. The distal-end region of the shaft carries a plurality of electrodes.
In a detailed aspect, the platelet inhibitor includes heparin, glycoprotein IIb/IIIa inhibitor and aspirin. In another detailed aspect, the distal-end region of the shaft includes an aperture and the distal-opening of the lumen network terminates at the outside surface of the shaft through the aperture. In still another detailed aspect, the aperture is carried by one of the electrodes. In a further detailed aspect, the lumen network includes a central lumen extending along the length of the shaft, and a plurality of branch lumens communicating with the central lumen at a first end and terminating at the outside surface of the shaft at a second end.
In another detailed aspect, the shaft includes a plurality of apertures, each coincident with one of the branch-lumen second ends. In yet another detailed aspect, the apertures are the same size. In still another detailed aspect, the apertures decrease in size progressively along the length of the shaft from the most distal aperture to the most proximal aperture. In a further detailed aspect, at least one of the plurality of apertures is carried by one of the electrodes. In yet a further detailed aspect, each pair of adjacent electrodes has at least one of the plurality of apertures located therebetween.
In another detailed aspect, the first mechanism is adapted to control the flow rate of the platelet inhibitor solution through the lumen network when in an xe2x80x9conxe2x80x9d position and to prevent the flow of platelet inhibitor solution when in an xe2x80x9coffxe2x80x9d position. In still another detailed aspect, the first mechanism includes a first variable pump located between the platelet-inhibitor-solution source and the proximal end of the lumen network. In a further detailed aspect, the proximal opening of the lumen network also communicates with a source of saline solution and the catheter further includes a second mechanism adapted to force the saline solution from the source through the at least one distal opening of the lumen network when the first mechanism is in an xe2x80x9coffxe2x80x9d position. In another detailed aspect, the second mechanism includes a second variable pump located between the saline solution source and the proximal end of the lumen network. In yet another detailed aspect, the second variable pump controls the flow rate of the saline solution through the lumen network. In still another detailed aspect, the catheter further includes a flow valve attached to the first and second variable pumps and adapted to switch between the first and second variable pumps.
In a third aspect, the invention relates to a catheter for use within a body cavity having biological fluid therein. The catheter includes a shaft having a proximal end, a distal-end region, and at least one recess on its outside surface. A soluble platelet inhibitor substance is located within the at least one recess and is adapted to elute upon contact with the biological fluid.
In a detailed aspect, the platelet inhibitor includes heparin, glycoprotein IIb/IIIa inhibitor, and aspirin. In another detailed aspect, the platelet inhibitor is dispersed within a matrix. In yet another detailed aspect, the matrix includes one of a porous matrix and a semi-porous matrix. In a further detailed aspect, the matrix consists of silicone. In another detailed aspect, the matrix includes a hydrogel. In still another detailed aspect, the hydrogel is selected from the group of polymers including polyacrylamide, polyvinyl pyrolidone, polyhydroxyethal methacrylate and polyvinyl alcohol. In a further detailed aspect, the catheter includes a layer of a heparin and a sugar-based solution mixture posited over the platelet inhibitor substance, the layer adapted to dissolve into the biological fluid. In a yet further detailed aspect, the catheter includes at least one electrode at the distal-end region of the shaft wherein the at least one recess is located on the outside surface of the at least one electrode. In another detailed aspect, the solubility of the platelet inhibitor substance increases with temperature through application of RF energy by an RF generator.
In a fourth aspect, the invention relates to a method of applying energy to biological tissue within a biological site. The method involves positioning a catheter having at least one electrode, and at least one pocket carried by the catheter having an opening terminating at the outside surface of the catheter, the pocket filled with a platelet inhibitor substance, within the biological site so that the electrode is adjacent the tissue to be ablated. RF energy is applied to the at least one electrode.
In a detailed aspect, the catheter has at least one pocket carried by a tubular wall of the catheter. In another detailed aspect, the at least one pocket is within the tubular wall. In still another detailed aspect, the at least one pocket is within the lumen defined by the tubular wall. In a further detailed aspect, the at least one pocket is carried by the at least one electrode.
In a fifth aspect, the invention relates to a method of applying energy to biological tissue within a biological site using a catheter having at least one electrode, and a lumen network carried by the shaft and having a proximal opening communicating with a source of platelet inhibitor solution and at least one distal opening terminating at an outside surface of the shaft. The method involves positioning the catheter within the biological site so that the electrode is adjacent to the tissue to be ablated. Energy is applied to the electrode while the platelet inhibitor solution is forced from the source through the at least one distal opening of the lumen network.
In a detailed aspect, the forcing of platelet inhibitor solution occurs during the application of energy. In another detailed aspect, the proximal opening of the lumen network communicates with a source of saline solution. The saline solution is forced from the source through the at least one distal opening of the lumen network. In yet another detailed aspect, the forcing of the saline solution occurs during the positioning of the catheter. In a further detailed aspect, the application of energy occurs intermittently within a time period having positions of xe2x80x9conxe2x80x9d power and xe2x80x9coffxe2x80x9d power periods wherein the forcing of saline solution occurs during xe2x80x9coffxe2x80x9d periods and the forcing of platelet inhibitor occurs during xe2x80x9conxe2x80x9d periods.
In a sixth aspect, the invention relates to a method of applying energy to biological tissue within a biological site. The method involves positioning a catheter having at least one electrode, and at least one recess carried by the catheter having an opening terminating at the outside surface of the catheter, the recess filled with a matrix having a platelet inhibitor substance dispersed therein. The catheter is positioned within the biological site so that the electrode is adjacent the tissue to be ablated. As energy is being applied to the at least one electrode, the platelet inhibitor substance is released from the at least one recess for eluting the platelet inhibitor substance within a biological fluid.
In a detailed aspect, the platelet inhibitor substance is eluted in the biological fluid after released from its stored position in a recess. In another detailed aspect, the matrix is a porous/semi-porous silicone. In a further detailed aspect, the platelet inhibitor substance is uniformly dispersed in a porous/semi-porous hydrogel matrix. In a still further detailed aspect, elution of the platelet inhibitor occurs when the biological fluid contacts the matrix.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention. These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.